1. Field of the Invention
The present invention relates to an ink jet recording apparatus used for recording information in the form of visual images and symbolic characters by means of ejecting ink droplets onto a recording medium such as paper sheets and so on.
2. Description of the Prior Art
An ink jet recording apparatus has several advantages. For instance, the level of noise generated by recording operations could be kept so low as to be neglible and common paper sheets can be used without processing and/or coating specific synthetic materials on the paper surfaces. There exist various kinds of ink jet ejecting methods used in the ink jet recording apparatus and in recent years, some of these methods have been put into practical uses.
Among these kinds of ink jet ejecting methods. one ink jet ejecting method, for instance, as described in Japanese Patent Application Laying-Open No. 51837/1979 has a different feature from that of other kinds of ink jet ejecting methods in that kinetic energy for ejecting ink droplets is obtained by means of transferring thermal energy into ink. In this ink jet ejecting method, a rapid voluminous change occurs in ink in accordance with a state transition of the ink caused by the thermal energy so that an ink droplet is ejected from an ejection outlet formed at the front of a recording head to form a flying ink droplet. The flying droplet reaches the surface of the recording medium and thus information recording can be established.
A recording head used in the above described ink ejecting methods, in general, has the ink ejection outlet for ejecting ink droplets and an ink liquid passage which communicates with the ink ejection outlet and which includes a heat process portion for transferring the thermal energy to ink so as to eject ink droplets from the ink ejection outlet. The heat process portion of the ink liquid passage has an electro-thermal coverting element for generating the thermal energy. The electro-thermal converting element has a resistance layer for heating and at least one pair of electrodes connected to the resistance layer. The resistance layer generates heat between said two electrodes by means of applying a voltage between said two electrodes. In this kind of a recording head, in general, forces applied into the ink of the ink liquid passage which are induced by capillary action, pressure drops or the like, are balanced so that a meniscus is formed in the ink liquid passage at the neighborhood of the ink ejection outlet. Every time an ink droplet is ejected, by means of the above mentioned balanced forces applied into ink, ink is supplied continuously into the ink liquid passage and a meniscus is formed again in the ink liquid passage at the neighborhood of the ink ejection outlet.
In the recording head with its structure described above, a few disadvantages exist.
The first disadvantages can be stated as follows. In order to make an ink ejection action stable, the pressure of ink contained in the ink liquid passage and other portions of the recording head should be kept in an appropriate value. In order to do so, various kinds of arrangements related to the recording head have been proposed. For example, the recording head and an ink tank for preserving ink which is connected to the recording head through a tube or the like are arranged in such a manner that their relative positions there between in a vertical direction are appropriately determined so that the pressure in the ink liquid passage may be kept in an appropriate value. However, in case that a shock is given to the recording head during transport of the recording apparatus or in case that a pressure fluctuation occurs in the inside of a cap while an ink ejection-outlet-disposed surface of the recording head is capped with the cap for preventing the evaporation of ink, the meniscus is moving downward from the neighborhood of the ink ejection outlet to the inside of the ink liquid passage due to a force generated by the shock and the pressure fluctuation applied to the ink. This phenomena is known as a loss of ink feed. In the loss of ink feed, the ink droplet can not be ejected regularly. Furthermore, in case of trying to continue to transfer thermal energy generated by the electro-thermal converting element into an empty portion of the ink liquid passage where ink is lost, the electro-thermal converting element may be even damaged due to heat concentration.
The second disadvantage relates to an increase of viscosity of ink. That is, in case that a viscosity of ink in the ink liquid passage is increased due to the evaporation of solvent components of ink through the ink ejection outlet of the recording head and so on, an ink ejection failure such as a decrease of the amount of the ejected ink droplet or non-election of ink occurs. Although an increase of viscosity of ink could be avoided to a certain extent by way of the capping as described earlier, such a way may not cope with this problem especially in case of trying ink ejection after a long period of time during which the ink ejection has not been performed.
The third disadvantage directs to bubbles generated in the ink. Small-sized bubbles in the ink generated by heat unused for ejecting ink droplets and bubbles mixed into ink from outside of the recording head through an ink supply passage member such as a tube may enlarge over a long period of time. In case that the enlarged bubbles exist in the ink liquid passage, there may occur the ink ejection failure such as a deflection of ejected ink droplet and the decrease of the amount of ejected ink droplet.
For resolving or preventing the first, second and third disadvantages described above, in some ink jet recording apparatuses, ejection recovery operations of the recording head or the like are performed. As for the ejection recovery operation, one approach is a suction method where ink in the ink liquid passage and other portions of the recording head is sucked to be discharged from the ink ejection outlet using a sucker pump and the other approach is an idle ejection method where the ink ejection is performed, independent of scheduled services of ink jet recording operations. A pressurizing method, similar to the suction method, is another approach where ink contained in the recording head is pressurized by pressure in the side of an ink supply passage to be discharged outside from the ink ejection outlet.
By means of the above mentioned suction method, pressurizing method or idle ejection method, high viscosity ink and the bubble growing in ink can be eliminated and also, by these ejection recovery operations which generate a force acting on ink contained in the recording head, the meniscus is returned to its regular position in the ink liquid passage so that the loss of ink feed can be overcome.
The ejection recovery operations described above or the like are done properly when an electric power source to the recording apparatus is put on or the recording operations of the recording apparatus begins. However, at the time when the ejection recovery operations or the like are done, it is not necessarily found that an abnormal state in the ink liquid passage and other portions of the recording head such as the loss of ink feed and the increase of viscosity of ink mentioned above occur. In case of doing such unnecessary ejection recovery operations or the like, ink is used wastefully as well as the recording efficiency goes down due to wasting time for doing such recovery operation.
With respect to overcoming the above mentioned drawbacks in applying the ejection recovery operations, for example, as found in Japanese Patent Application Laying-Open No. 98542/1986, disclosed is a structure for detecting temperature of the recording head and for knowing a presence of the abnormal state based on the detected temperature. In this prior art structure, it is possible to execute the ejecting recovery operation, only when the abnormal state is found in the ink liquid passage and so on. However, the detection of abnormality is not directed to individual parts of a plurality of the ink liquid passages. In case that the abnormal state exists in a relatively small number of the ink liquid passages among all of them, the temperature change which occurs in the overall recording head by above mentioned small abnormal state is hard to be detected, therefore, it is difficult that the abnormal state is detected.
With respect to overcoming the above mentioned problem in abnormality detection which should be resolved, for example, a structure disclosed in Japanese Patent Application Laying-Open No. 14967/1984 can be taken to be one approach to the solution. In the disclosed structure, by means of supplying the electric energy into the electro-thermal converting element for generating thermal energy for ejecting ink droplet, this electric energy being not enough to make ink drops ejected, temperature change is caused. And the abnormal state in the ink liquid passage is examined by detecting fluctuation of the electric energy being supplied into the electro-thermal converting element which is adversely caused by the above mentioned temperature change. In this structure for detecting the abnormal state, the abnormal state in the individual ink liquid passage can be detected separately by sensing up the electric current through the individual electro-thermal converting element.
However, because the above additive electric energy supplied to the electro-thermal converting element for detecting the abnormal state is taken to be low enough so that the energy may not contribute to ink droplet ejection, it takes a relatively longer time to detect a significant change in the electric energy induced by the temperature change caused by the additive electric energy. So far, it takes a longer time to detect the abnormal state, and because a number of fine-sized bubbles are generated by heat generated in ink while the electric energy is supplied continuously into the electro-thermal converting element for a relatively long time, these fine-sized bubbles may exert a bad influence on the ink droplet ejection. In addition, because detection procedures of the abnormal state are made independently of the ejection recovery operations, an occurrence of time spent for the detection procedures brings a lowering of efficiency of the overall recording procedures. And furthermore, a specific structure is required to supply the additive electric energy as low as the ink droplet ejection never occurs.